Up to now, a thermal detection device and a quantum detection device have been known as electromagnetic wave detection devices for a frequency band ranging from a millimeter wave band to a terahertz wave band (equal to or more than 30 GHz and equal to or less than 30 THz). Examples of the thermal detection device include a microbolometer (a-S1 or VOX), a pyroelectric device (LiTaO3 or TGS), and a Golay cell. The above-mentioned thermal detection device converts, into heat, a change in property which is caused by an electromagnetic wave energy, and then converts a change in temperature into a thermoelectromotive force or a resistance to detect the change in property. The thermal detection device does not necessarily require cooling but has a relatively slow response because of heat exchange. Examples of the quantum detection device include an intrinsic semiconductor device (such as MCT(HgCdTe) photoconduction device) and an extrinsic semiconductor device. The quantum detection device captures an electromagnetic wave as a photon and detects a photoelectromotive force of a semiconductor having a small band gap or a change in resistance thereof. The quantum detection device has a relatively quick response but requires cooling because thermal energy at room temperature in the frequency range cannot be neglected.
In recent years, an electromagnetic wave detection device using a rectifier for the frequency band ranging from the millimeter wave band to the terahertz wave band (equal to or more than 30 GHz and equal to or less than 30 THz) has been developed as a detector which has a relatively quick response and does not require cooling. The detector captures an electromagnetic wave as a high-frequency electrical signal and detects the high-frequency electrical signal which is received from an antenna and rectified by the rectifier. According to such a system, as the frequency band becomes higher, the detection is normally more difficult. This is because, as the frequency band becomes higher, filter effects caused in all portions of the detector cannot be neglected. Therefore, in many cases, there is employed a system in which the antenna is directly coupled to a rectifier having a microstructure to suppress the filter effects.
Japanese Patent Application Laid-Open No. H09-162424 discloses the detector as described above. The rectifier is a Schottky barrier diode having a Schottky electrode area set to 0.0007 μm2 (0.03 μm in diameter) by micro-machining, which detect an electromagnetic wave of approximately 28 THz (10.6 μm in wavelength) by a CO2 laser. It is known that the Schottky barrier diode is provided with an Rc low-pass filter having a junction capacitance Cj in a Schottky barrier and a series resistance Rs. The junction capacitance Cj is proportional to the Schottky electrode area. Therefore, the simplest method of increasing a cutoff frequency fc (=(2π×RsCj)−1) may be a reduction in Schottky electrode area. Such a relationship of a typical Schottky barrier diode is calculated as follows. When the Schottky electrode area is set to 1 μm2 (approximately 1 μm in diameter) by micro-machining, fc is estimated to be approximately 300 GHz. When the Schottky electrode area is set to 0.1 μm2 (approximately 0.3 μm in diameter) which is 1/10 of above by micro-machining, fc is estimated to be approximately 3 THz. When the Schottky electrode area is set to 0.01 μm2 (approximately 0.1 μm in diameter) which is 1/10 of above by micro-machining, fc is estimated to be approximately 30 THz.